JPH07218038A - Heat transfer tube for mixed refrigerant - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a heat transfer tube which promotes heat transfer by promptly eliminating a condensed liquid film and which can obtain a high heat transfer coefficient even when a non-azeotropic mixed refrigerant is used. A heat transfer tube 6 having a spiral groove on the inner surface that is horizontally attached to a heat exchanger, in which, in addition to the inner surface groove 1, a space 3 serving as a liquid pool is provided on the inner surface of the tube, and the shape of the space 3 is formed in the flow direction. Inner surface processing heat transfer tube with different temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat transfer tube used in a heat exchanger of a refrigerating apparatus or an air conditioner using a non-azeotropic mixed refrigerant, and an inner surface processing suitable for an application in which the fluid in the tube undergoes a phase change in the tube. Regarding tubes.

[0002]

2. Description of the Related Art Conventionally, as one of methods for promoting heat transfer inside a tube, there is an inner grooved tube in which a large number of fine grooves are spirally formed on the inner surface of the heat transfer tube. The heat transfer coefficient obtained when the refrigerant flows while changing the phase in this heat transfer tube is much higher than that of the smooth tube, and the one that improves the performance by changing the groove shape, depth, twist angle, etc. Many have been proposed.

In order to promote heat transfer in the condensation process, a new heat transfer surface should always be created for the refrigerant vapor, and for that purpose the condensed liquid film must be quickly removed. For this reason, it is said that it is desirable that the crest angle of the crest of the inner surface groove is sharp and the shape of the trough is such that the condensate can be easily drawn.
On the contrary, in the evaporation process, it is important to cover the heat transfer surface with a thin liquid film to increase the effective heat transfer surface. For this,
A groove shape that allows the liquid refrigerant to be easily supplied to the top of the tube, which is easy to dry, is required. Although the concept of heat transfer promotion is different between condensation and evaporation, many air conditioners are currently used as heat pumps, so it is desirable that the heat transfer tubes used for these have high performance in both condensation and evaporation. One example of the structure of the inner surface spiral groove is a heat transfer tube of Japanese Patent No. 1181228, and as an example of a structure other than the continuous spiral groove, a heat transfer tube provided with a groove divided into two as described in JP-A-2-161267, JP-A-60-263096 discloses an evaporation tube in which a contact surface is increased by inserting a thin-walled cylindrical body having an inner diameter slightly smaller than the inner diameter into the surface.

However, these have been optimized for a single refrigerant as a working medium. The heat transfer performance of the inner grooved tube of non-azeotropic mixed refrigerant of two-component and three-component system is improved without exception when the smooth tube is used as a reference, but the performance deterioration due to mixing cannot be recovered depending on the combination of refrigerants. There is also.

As a measure for improving the heat transfer performance, in addition to using the inner spiral grooved tube, the following can be considered. That is, FIG. 11 shows an example of the heat transfer characteristics of the non-azeotropic mixed refrigerant in the inner grooved tube. In the figure, the horizontal axis represents the mass velocity (kg / m ² s) and the vertical axis represents the average heat transfer coefficient (kW / m ² K). From this figure, it can be seen that the heat transfer characteristics of the non-azeotropic mixed refrigerant are more affected by the mass velocity than the single refrigerant, and the results of the single refrigerant approach as the mass velocity increases. Utilization in a high mass velocity range to obtain high heat transfer performance can also be used as an effective means.

[0006]

When a non-azeotropic mixed refrigerant in which a plurality of kinds of refrigerants having different boiling points are mixed is used in the current heat exchanger, various disadvantages occur. This is a decrease in effective temperature difference due to a change in concentration and a change in saturation temperature during the phase change process, and a decrease in heat transfer performance.

FIG. 9 shows a vapor-liquid equilibrium diagram of a binary non-azeotropic mixed refrigerant. The process of phase change of mixed refrigerant under constant pressure is illustrated by this figure. The horizontal axis in the figure shows the high boiling point refrigerant A.
Shows the mixed composition ratio of the low-boiling-point refrigerant B to, and the vertical axis shows the temperature. The part surrounded by the two curves is the saturation region,
The upper part of the dew point curve shows the superheated region, and the lower part of the boiling point curve shows the supercooled region. Generally, the phase change inside the condenser begins to condense on the line of composition y in the figure from the superheated region at point a, and b
Described as completed in points. In addition, there is an idea that the low boiling point component B is actually supercooled to the b'point where it becomes 1 and the condensation is completed. According to the latter idea, the bulk temperature of the condensate is supercooled, and the component of the refrigerant vapor has many low-boiling point components B, so the effective temperature difference is small, and a large temperature difference is required considering it as a heat exchanger. Will be.

10 (a) and 10 (b) are experimental results of heat transfer inside a tube of a mixed refrigerant of condensation and evaporation and a single refrigerant, respectively. The dryness is plotted on the horizontal axis and the local heat transfer coefficient is plotted on the vertical axis. This is shown here. As shown in the figure, the non-azeotropic mixed refrigerant is
The heat transfer performance tends to decrease in both condensation and evaporation within a specific dryness range. In order to improve the overall heat transfer performance, a heat transfer promotion method that can recover the reduced amount is required. Therefore, in the present invention, in the condensing process, the condensate is promptly removed from the heat transfer surface to separate and flow from the refrigerant vapor to accelerate the flow rate,
By providing a high heat transfer coefficient over the entire length of the heat exchanger and increasing the effective heat transfer surface even in the evaporation process, a heat transfer tube with less performance deterioration even with a non-azeotropic mixed refrigerant is provided.

[0009]

In order to solve the above problems, the present invention provides a spiral groove on the inner surface of a heat transfer tube or a heat transfer surface processed to promote heat transfer, and also forms a void on the inner surface of the tube. , The ratio of the voids in the cross section of the refrigerant channel is changed in the flow direction.

[0010]

With the above structure, in addition to the effect of promoting heat transfer due to the swirling flow generated by the inner surface groove, the liquid film can be easily removed from the heat transfer surface by allowing the condensed liquid film to flow into the gap.
Further, since the flow passage cross section changes in the flow direction, the flow velocity is prevented from decreasing. Further, in the case of evaporation, the liquid refrigerant enters the voids and flows, so that the contact area increases and a high heat transfer coefficient is provided.

[0011]

【Example】

(Embodiment 1) A first embodiment of the present invention will be described below with reference to the drawings. 2 is a perspective view showing an embodiment of the present invention partially broken away, and FIG. 1 is a sectional view taken along the line AA of FIG. The inner surface processing tube of the present invention is mounted horizontally with respect to the heat exchanger. An air gap 3 is formed at the bottom of the inner surface of the heat transfer tube by the fin 2, and the inner surface groove 1 is also formed continuously with the fin 2. In the case of condensation, the refrigerant vapor flows in from the direction of the white arrow in FIG. 2 and condenses on the heat transfer surface where the inner groove is formed and flows in a gas-liquid two-phase state. In the case of evaporation, the direction of the hatched arrow is opposite. Flows in from.

Next, FIGS. 3 (a), (b) and (c) show examples of the shape of the fin for forming the void 3 of this embodiment. Figure 3
(A), (b) and (c) are cross-sectional views of the inner surface processed pipe in the present embodiment taken along a plane perpendicular to the pipe axis. In FIG. 3A, the fins 2 are formed along the pipe inner wall from the pipe bottom portion to the left and right, and a gap 3 is formed between the pipe inner wall and the fins. In FIG. 3B, fins are formed along the bottom of the tube from the side surface of the inner wall of the tube. In FIG. 3C, fins are formed along the inner wall of the pipe in opposite directions from the bottom and top of the pipe.

The material of the fins forming the gap may be the same as the material of the heat transfer tube or may be a porous material of a different metal. If the fins are formed by using a metal porous body, not only the fins contribute to the heat transfer surface but also the liquid refrigerant is easily held, so that the condensed liquid film can be easily removed.

The surface of the fin has a groove formed in the same direction as the groove on the inner wall of the pipe so as not to disturb the swirling flow of the refrigerant vapor. Further, examples of the shape in the tube axis direction are shown in FIGS. In this figure, the fin 2 shown in FIG. 3 is cut away from the root and displayed. As shown in FIG. 4, it is easy to remove the liquid film into the void by forming it in a saw shape or providing a slit. In the examples shown in FIGS. 3A, 3B, and 3C, the size of the void 3 is changed by changing the angle of the fin and the length from the root.

According to the present embodiment, in the condensation process, the condensate flows down the groove and is removed in the void provided at the bottom of the heat transfer tube.
Due to this effect, a new heat transfer surface can always be provided for the refrigerant vapor. Figure 2 shows the proportion of voids in the cross-sectional area of the pipe.
As shown in, it is configured so as to gradually increase in the flow direction of the refrigerant. The liquid refrigerant collected in the gap is supercooled while passing through this flow path and flows to the outlet of the condenser.
On the contrary, since the flow path of the refrigerant vapor gradually narrows in the flow direction of the refrigerant, the condensation proceeds without reducing the flow velocity.

Also, in the evaporation process, the refrigerant is throttled by the expansion valve to become a gas-liquid two-phase and flows into the heat transfer tube with a low degree of dryness. The shape of the inner surface of the heat transfer tube of the present embodiment at the beginning of the evaporation process has a structure in which the ratio of the gaps formed by the fins is considerably large and the tube cross section is divided into a plurality of sections.
Since the fins are thermally connected to the heat transfer tube wall, they contribute as a heat transfer surface, and the gap between the fins and the inner wall is small where the dryness is high, and the liquid refrigerant held in the gap is efficiently evaporated. You can

As a general method for manufacturing a tube with an inner spiral groove, a method is used in which the inner surface of the tube is pulled out while being processed. However, although the heat transfer tube having the inner surface structure as in this embodiment cannot be manufactured by the above manufacturing method, it can be manufactured by a method of forming a fin or a grooved flat plate into a circular shape and welding it. If a plurality of flat plates are used when forming and welding the processed flat plate, it becomes possible to manufacture a heat transfer tube having a more complicated inner surface shape.

In order to assemble the heat transfer tube of the present invention into a cross fin tube type heat exchanger, there is a pipe expanding step in which pressure is applied from the inner surface of the heat transfer tube to bring the heat transfer tube and the laminated fin into close contact with each other. Conventionally, a mechanical pipe expanding method in which a plug is pushed into a pipe has been adopted, but in this method, the pipe is expanded while crushing the ridges of the inner surface groove, so that the shape of the inner surface is limited to some extent.
However, since a tube expansion method using a fluid as described in Japanese Patent Laid-Open No. 4-316991 has been developed at present, it is possible to perform complicated processing on the inner surface of the heat transfer tube.

To facilitate the discharge of the condensate, the heat transfer tube is attached to the heat exchanger while being inclined in the flow direction of the refrigerant. In the case of condensation, if it is inclined downward in the flow direction, it is easy to convey the condensate in the flow direction of the refrigerant even if the flow rate is small.

Another method for obtaining the same effect is shown in FIG.
A cocoon-shaped heat transfer tube having a cross section as shown in FIG. In the condensation process, the refrigerant is condensed in the upper channel and the condensate is passed in the lower channel. It is also conceivable to provide fins on the inner surface of an elliptical heat transfer tube as shown in FIG. 5 (b) to partition the flow path, and arrange the flow path vertically.

When the condensation process progresses to a composition in which the low boiling point component is concentrated on the gas phase side, the dew point temperature decreases. As shown in FIG. 8, the dryness of the refrigerant is low in this region, and the proportion of the liquid refrigerant is large, so that the refrigerant vapor has a flow pattern intermittently flowing in the upper portion of the heat transfer tube. In order to efficiently perform heat exchange, it is necessary to obtain a lower heat source or to apply a heat transfer promotion method in order to condense the refrigerant vapor having a lower dew point temperature at the upper part of the inner surface of the tube. In order to achieve this purpose other than processing on the inner surface of the pipe, it is conceivable to process the air-side fins so that heat can be easily transferred to the upper flow path side where the refrigerant vapor easily flows when installed in the heat exchanger. .

(Embodiment 2) FIG. 6 is a sectional view of an inner surface processing pipe according to another embodiment of the present invention. A thin plate cylindrical body 7 having a spiral shape or a horizontal slit formed in the tube axis on the inner surface of the heat transfer tube.
Is inserted and is joined to the mountain portion 8 of the groove formed on the inner surface of the heat transfer tube. Instead of the thin plate cylindrical body shown in FIG. 7B, a thin plate as shown in FIG. 7A may be spirally wound.

This embodiment also has the effect of efficiently removing the liquid refrigerant during condensation and the effect of efficiently evaporating the liquid refrigerant held in the gap between the thin plate insert 7 and the inner surface groove 8 during evaporation. As in the case of the first embodiment, it is possible to suppress performance deterioration when a non-azeotropic mixed refrigerant is used.

(Embodiment 3) FIG. 12 shows a sectional view of a heat transfer tube of a third embodiment perpendicular to the tube axis. As shown in the first embodiment, a void 3 is formed in the bottom of the inner surface of the heat transfer tube by the fin 2, and a protrusion 11 is provided on the outer surface of the heat transfer tube on the side of the void. In the heat transfer tube of the first embodiment, the structure inside the tube is vertically asymmetric with respect to the flow direction of the refrigerant, and the difference in density between the refrigerant vapor and the liquid refrigerant is used to separate gas and liquid. When assembling such a heat transfer tube as a heat exchanger, it is a very important step to align the upper and lower positions of the heat transfer tube. Therefore, by attaching the projections 11 to the outer surface of the tube, the vertical position of the heat transfer tube can be easily known. Also, the protrusion 1 on the fin side
Providing a collar with a recess that fits in 1 can prevent mistakes when assembling into the heat exchanger. Furthermore, by providing such protrusions 11, it is possible to improve the drainage performance of the heat exchanger during defrosting. Such protrusions can be easily made in the manufacturing process of welding the heat transfer tubes.

[0025]

According to the present invention, high heat transfer performance can be obtained during condensation. That is, the condensate liquid film flows down along the inner surface grooves and is eliminated in the voids, and always gives a new heat transfer surface to the refrigerant vapor. Further, the voids are sufficiently large with respect to the condensed liquid and serve as a liquid pool, so that the liquid refrigerant is prevented from rising along the inner surface groove to the pipe wall and becoming a thermal resistance. Since the wall surface forming the void is also an expanded heat transfer surface, the liquid refrigerant is effectively cooled therein. Further, since the flow path of the refrigerant vapor becomes narrower in the flow direction, the phase change proceeds without significantly reducing the flow velocity.

In the case of evaporation, the ratio of the voids formed by the fins and the tube wall fins is considerably large, and the tube cross section is divided into a plurality of sections. Since the fins are thermally connected to the heat transfer tube wall, they contribute as a boiling heat transfer surface.

Therefore, even when a non-azeotropic mixed refrigerant is used, it is possible to suppress a decrease in the condensation heat transfer coefficient.

[Brief description of drawings]

FIG. 1 is a partial sectional view of a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is an explanatory diagram of an example of the shape of the fin according to the first embodiment of this invention.

FIG. 4 is an explanatory view of an example of the shape of the fin in the tube axis direction of the first embodiment of the present invention.

FIG. 5 is an explanatory diagram of a shape example of the heat transfer tube according to the first embodiment of this invention.

FIG. 6 is a cross-sectional view perpendicular to the tube axis of the second embodiment of the present invention.

FIG. 7 is an explanatory view of a thin plate insert body according to a second embodiment of the present invention.

FIG. 8 is an explanatory diagram of a flow pattern at low dryness.

FIG. 9 is a vapor-liquid phase equilibrium diagram of a non-azeotropic mixed refrigerant.

FIG. 10: Heat transfer characteristics of non-azeotropic mixed refrigerant (effect of dryness)
Fig.

FIG. 11 is a diagram of heat transfer characteristics (effect of mass velocity) of a non-azeotropic mixed refrigerant.

FIG. 12 is a cross-sectional view perpendicular to the tube axis of the third embodiment of the present invention.

[Explanation of symbols]

1 ... Inner surface groove, 2 ... Fin, 3 ... Void, 4 ... Upper flow path, 5
... lower flow path, 6 ... heat transfer tube, 7 ... thin plate cylinder, 8 ... inner surface groove portion, 9 ... refrigerant vapor, 10 ... liquid refrigerant, 11 ... protrusion.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Kusumoto 502 Kintatemachi, Tsuchiura City, Ibaraki Prefecture

Claims (1)

[Claims] 1. A heat transfer tube for a mixed refrigerant, which is a heat transfer tube in which spiral continuous grooves are formed on the inner surface of the tube, and narrow gaps are formed on the side surface and the bottom of the inner wall.